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https://issues.apache.org/jira/browse/SOLR-13898?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16972682#comment-16972682
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Ben Manes commented on SOLR-13898:
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Since {{computeIfAbsent}} is complex and so are the LRU & LFU caches, I
wouldn't have felt confident enough to add an implementation. Of course I am
less familiar with Solr's code, so Instead I would have used a racy version
(ala {{ConcurrentMap}}) rather than an atomic version. Then it is just
refactoring of code structure for taking advantage of atomicity if supported by
the {{SolrCache}}. Since those versions would go away in 9.x and no one
complained, it seems okay to be conservative. But if you're comfortable, it is
great to do for current users.
> Non-atomic use of SolrCache get / put
> -------------------------------------
>
> Key: SOLR-13898
> URL: https://issues.apache.org/jira/browse/SOLR-13898
> Project: Solr
> Issue Type: Bug
> Security Level: Public(Default Security Level. Issues are Public)
> Affects Versions: 8.3
> Reporter: Andrzej Bialecki
> Assignee: Andrzej Bialecki
> Priority: Major
> Fix For: 8.4
>
> Attachments: SOLR-13898.patch, SOLR-13898.patch
>
>
> As pointed out by [~ben.manes] in SOLR-13817 Solr code base in many key
> places uses a similar pattern of non-atomic get / put calls to SolrCache-s.
> In multi-threaded environment this leads to cache misses and additional
> unnecessary computations when competing threads both discover a missing
> value, non-atomically compute it and update the cache.
> Some of these places are known performance bottlenecks where efficient
> caching is especially important, such as {{SolrIndexSearcher}},
> {{SolrDocumentFetcher}}, {{UninvertedField}} and join queries .
> I propose to add {{SolrCache.computeIfAbsent(key, mappingFunction)}} that
> will atomically retrieve existing values or compute and update the cache.
> This will require also changing how the {{SolrCache.get(...)}} is used in
> many components.
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